Vehicle brake



g- 1939- v. NQICOLET ET AL 2,168,845

VEHICLE BRAKE Filed Jan. 6, 1958 J7me Tue 5,

1-2. law/$ 54.61:

Patented Aug. 8, 1939 VEWCLE Victor Nicolet and tart usselet, Paris, France Application .lanuary 6, 1938, Serial No. M33317 In France January 13, 1937 The present invention relates to a braking device for vehicles, particularly for railway vehicles, though not limited to this particular application.

In order that a vehicle brake should never cause skidding due to locking of the wheels it is necessary to obtain at all times the condition the braking force by which the brake shoes or blocks are applied to the wheels, I the coeflicient of friction between the frictional surfaces,

and o the coeflicient of adhesion of the wheel.

or the axle.

The eflicacy of such a brake will thus be limited by these conditions, and it will be a maximum if at any time during the braking process 20 the braking force Q is adjusted to a value 45 active surface, consists of asbestos material in frictional contact with the steel of the tires, the coefiicient I will be practically independent of the speed, and-thus the ratio will increase when the speed diminishes, and it would be necessary in achieving the same end 55 to increase the braking force when slowing down.

where P is the weight of the braked vehicle, Q

n the contrary, if use is made of shoes whose.

In practice, the braking force is given a constant value which is less than the lower limit of in order that theoretically there shall only bea tendency for skidding to take place when stopping, or alternatively at a speed greater than the maximum speed of. the vehicle to be braked, depending on the direction of the variation of with the speed, but in either case the optimum braking effect is not constantly obtained over the whole speed range.

The invention has for its object to obviate this serious drawback, and it consists in employing upon a given vehicle frictional surfaces consisting of difierent materials for which the ratio varies in opposite directions with the speed, and thus by properly combining these frictional surfaces making possible a. combined or resultant ratio which is practically constant over the required speed range. The brr king force Q can then be fixed at a constant value which is quite near its upper safety limitthis latter being itself practically constant since P is a constant. Consequently, in accordance withthe principles initially stated the optimum braking effect will always be obtained without the addition of any automatic regulating devices and without the necessityof varying the I braking force when slowing down. These different frictional surfaces may be used in the form of shoes or linings of any kind, or of drums or tires, and the materials used may be various so long as they have coefficients of friction which vary with the speed according to different formulae so as to contribute collectively to the desired result.

The accompanying drawing shows by way of example an embodiment of the invention.

In the example herein represented, which .shows the application ofthe invention to a railway vehicle,- each of the usual shoes of 9. ve-- shoe of cast iron and that of the asbestos mal terial is equal to the inverse ratio of the dis tances from the respective pivot axes 6-4 to the line of application of the force A--B passing through the axis 2. In the present device, this ratio is about 3:1, that is the shoe 4 is applied to the rim 8 with a force which is three times the force with which the shoe 5 is applied. As has been established by experiments, the permis- Sible coemcient (p of adhesion between the wheels and the rails can be assumed as 0.11 at 60 miles per hour and as 0.17 at 10 miles per hour. The coemcient of friction between a brake shoe and the wheel may be assumed for cast iron shoes as ,fI=0.11 at 60 miles per hour and as 0.24 at 10 miles per hour, the corresponding values IA for asbestos shoes being 0.35 and 0.3 respectively.

Thus, with the assumption of the dependency on the speed being substantially linear within the considered limits, we obtain the following formulas for the respective coeflicients, 0 being the speed of travel:

=0.182 (1-12/150) 11:0.266 (1-v/100) JA==0.290 (1+v/300) 0.266a+ 0.29b= 0.266'ma- 0.29mi) The proportion 3:1 chosen in the example as illustrated gives a good approximation to this v ue,

By properly selecting azb, 1--e could be made fully independent of the speed, if, as we assumed, the various coeflicients were linear functions of the speed. Actually this is so nearly true that it has been found that at a certain brake cylinder pressure, the skidding limit is only approached when the speed of the vehicle is above :15 miles per hour and when the vehicle is already stopping, in which latter case, of course, no actual skidding will occur. i I I e As the behaviour of the shoes of asbestos material is unfavourably afiected by moisture it is advantageous to arrange the cast iron shoes 4 below the shoes of asbestos material 5, in order that these cast iron shoes may destroy the film of water which covers the tire in case of .rain.

Having now described our invention, what we claim as new and desire to secure-by Letters Patent is l 1. A vehicle brake mechanism, including a wheel, a brake member comprising two brake surfacesof different material, adapted to cooperate with said wheel, the rate of variation in accordance with the speed of the coeiiicient of friction being more negative for the material of one of the surfaces and less negative for the other surface, than the rate at which the coefiicient of adhesion between the wheels and the rolling surface varies in accordance with the speed of the vehicle, force distributing arrangements being further provided for so distributing to the two brake surfaces the totalapplication forcedzhat the joint coeflicient of friction in respect to the total force of application varies in accordance with the vehicle speed at the same rate as the coeiiicient of adhesion.

2. Vehicle brake as claimed in claim 1, in which one brake surface of asbestos mass and another brake surface of cast iron are arranged to co operate with a steel surface the cast iron surface being applied with about three times the force by which the asbestos surface is applied.

3. A vehicle brake mechanism, including a wheel having a steel rim, a brake member having two brake shoes carried therebyi and adapted to be applied to said steel rim, one brake shoe comprising a braking surface of asbestos mass and the other brake shoe comprising a braking surface of cast iron, force distributing means for applying the shoe having the castiron surface with three times the force by which the shoe comprising the asbestos mass surface is applied ,the shoe comprising the cast iron surface being placed below the shoe comprising the asbestos surfacen VICTOR NICOLET. ROBERT ROUSSELET. 

